Math Problem Statement

Diketahui pasangan himpunan berurutan: f = {(3, -4), (1, 8), (2, -5), (0, 4), (10, 1)} dan (f o g) = {(2, 8), (1, -5), (0, -4), (3, 4)}. Tentukan: a. g b. (g o f)

Solution

We are given two functions: ff and fgf \circ g in the form of ordered pairs. To determine gg, we can use the relation fg(x)=f(g(x))f \circ g(x) = f(g(x)), which gives us a clue for calculating the corresponding values of gg.

Problem breakdown:

  • f={(3,4),(1,8),(2,5),(0,4),(10,1)}f = \{(3, -4), (1, 8), (2, -5), (0, 4), (10, 1)\}
  • fg={(2,8),(1,5),(0,4),(3,4)}f \circ g = \{(2, 8), (1, -5), (0, -4), (3, 4)\}

We need to:

  1. Determine the function gg.
  2. Verify the composition gfg \circ f.

Step-by-step solution:

Part a: Finding gg

Since fg(x)=f(g(x))f \circ g(x) = f(g(x)), we know that the output of f(g(x))f(g(x)) must match the second element of each pair in fgf \circ g. Let's find g(x)g(x) for each pair:

  1. From fg(2)=8f \circ g(2) = 8, we need f(g(2))=8f(g(2)) = 8. In the function ff, f(1)=8f(1) = 8. Therefore, g(2)=1g(2) = 1.
  2. From fg(1)=5f \circ g(1) = -5, we need f(g(1))=5f(g(1)) = -5. In the function ff, f(2)=5f(2) = -5. Therefore, g(1)=2g(1) = 2.
  3. From fg(0)=4f \circ g(0) = -4, we need f(g(0))=4f(g(0)) = -4. In the function ff, f(3)=4f(3) = -4. Therefore, g(0)=3g(0) = 3.
  4. From fg(3)=4f \circ g(3) = 4, we need f(g(3))=4f(g(3)) = 4. In the function ff, f(0)=4f(0) = 4. Therefore, g(3)=0g(3) = 0.

Thus, the function gg is: g={(2,1),(1,2),(0,3),(3,0)}g = \{(2, 1), (1, 2), (0, 3), (3, 0)\}

Part b: Finding gfg \circ f

To find gf(x)=g(f(x))g \circ f(x) = g(f(x)), we apply the function gg to the output of f(x)f(x):

  1. f(3)=4f(3) = -4, but g(4)g(-4) is undefined, so this pair does not contribute.
  2. f(1)=8f(1) = 8, but g(8)g(8) is undefined, so this pair does not contribute.
  3. f(2)=5f(2) = -5, but g(5)g(-5) is undefined, so this pair does not contribute.
  4. f(0)=4f(0) = 4, but g(4)g(4) is undefined, so this pair does not contribute.
  5. f(10)=1f(10) = 1, and g(1)=2g(1) = 2. Therefore, gf(10)=2g \circ f(10) = 2.

Thus, the only valid pair for gfg \circ f is: gf={(10,2)}g \circ f = \{(10, 2)\}

Summary:

  • g={(2,1),(1,2),(0,3),(3,0)}g = \{(2, 1), (1, 2), (0, 3), (3, 0)\}
  • gf={(10,2)}g \circ f = \{(10, 2)\}

Let me know if you'd like any further details or explanations!


Here are some related questions for further exploration:

  1. How do you generalize the process of finding the inverse of a function composition?
  2. What happens when a function is not injective or surjective? How does it affect compositions?
  3. Can we always find gg given fgf \circ g and ff? What if some values of ff are undefined?
  4. What are the conditions for two functions to be composable in terms of their domain and codomain?
  5. How can the concept of function composition be extended to multiple functions, e.g., fghf \circ g \circ h?

Tip: Function composition is only possible if the output of the second function is a valid input for the first one, so always check their domains carefully!

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Math Problem Analysis

Mathematical Concepts

Function Composition
Ordered Pairs
Mapping

Formulas

f o g(x) = f(g(x))

Theorems

Function Composition Definition

Suitable Grade Level

Grades 10-12